Abstract. Due to the important contribution of nitrous acid (HONO) to OH radicals in
the atmosphere, various technologies have been developed to measure HONO.
Among them, wet-denuder–ion-chromatography (WD/IC) is a widely used
measurement method. Here, we found interferences with HONO measurements by
WD/IC based on a comparison study of concurrent observations of HONO
concentrations using a WD/IC instrument (Monitor for AeRosols and Gases in
ambient Air, MARGA) and long-path absorption photometer (LOPAP) at the
Station for Observing Regional Processes of the Earth System (SORPES) in
eastern China. The measurement deviation of the HONO concentration with the
MARGA instrument, as a typical instrument for WD/IC, is affected by two
factors. One is the change in denuder pH influenced by acidic and alkaline
gases in the ambient atmosphere, which can affect the absorption efficiency
of HONO by the wet denuder to underestimate the HONO concentration by up to
200 % at the lowest pH. The other is the reaction of NO2 oxidizing
SO2 to form HONO in the denuder solution to overestimate the HONO
concentration, which can be increased by to 400 % in denuder solutions with the highest pH values due to ambient NH3. These processes are in
particularly important in polluted east China, which suffers from high concentrations of SO2, NH3, and NO2. The overestimation
induced by the reaction of NO2 and SO2 is expected to be of growing importance with the potentially increased denuder pH due to the decrease in SO2. We further established a method to correct the HONO data measured
by a WD/IC instrument such as the MARGA. In case a large amount WD/IC-technique-based instruments are deployed with the main target of monitoring the water-soluble composition of PM2.5, our study can help to obtain a
long-term multi-sites database of HONO to assess the role of HONO in
atmospheric chemistry and air pollution in east China.
Chiral Selectors in Capillary Electrophoresis: Trends During 2017–2018